1. Field of the Invention
The present invention relates to a line commutation type fault current limiter, and more particularly, to a line commutation type fault current limiter which can reduce manufacturing and maintenance costs, carry out line commutation by operating a cutoff switch by fault current energy, respond rapidly to a fault, be immediately restored to an original state, and perform either an active or a passive operation.
2. Discussion of the Related Art
An electric power system uses a fault current limiter to prevent an overcurrent exceeding a threshold value from flowing into the system when an accident such as a lightning strike, a ground fault, or a short circuit occurs.
The most important factors in a line commutation type fault current limiter are a fault sensing scheme and a cutoff switch driving scheme. Fault is generally sensed using an external fault sensing device and a cutoff switch is opened by operating a cutoff switch driving device to perform line commutation. For such a method, the line commutation type fault current limiter should additionally include the external fault sensing device and the cutoff switch driving device. Moreover, external energy is needed to drive the cutoff switch, and a semiconductor switch for a large quantity of current or a large-capacity energy storage device is demanded, thereby increasing manufacturing costs.
To solve such problems, a method is used for operating the cutoff switch using fault current energy without the need of an additional energy source or the cutoff switch driving device. In this method, if a superconducting fault current limiting element connected serially to the cutoff switch is quenched by a fault current and therefore generates resistance, the current is bypassed to a cutoff switch driving coil. Then a repulsive force generated by a magnetic field of the coil and a current induced to an adjacent metal conductor acts directly on the cutoff switch to open the cutoff switch and complete line commutation. Thereafter, the fault current limiting unit limits the current. However, since this method requires a superconductor manufactured to endure a rated current and a cooling device for the superconductor, installation and maintenance costs are raised. Furthermore, since this method uses passive elements, it is difficult to actively operate constituent elements according to a usage condition.